Methods and apparatus for determining transmission power levels

ABSTRACT

Methods and apparatus are provided for determining transmission power levels. The power characteristics of a cable modem family are determined by testing cable modems in a cable modem family with various downstream frequencies and transmission power levels to determine internal gain levels. The power characteristics of the cable modem family can then be stored in an efficient manner in each cable modem by using interpolation. The individual cable modem can then be characterized by testing the cable modem with a limited set of downstream frequencies and transmission power levels to determine an internal gain level offset for that particular cable modem. With the power characteristics table, internal gain level offset, and interpolation, transmission power levels can be determined during network operation when downstream frequencies and internal gain levels are known.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates generally to determining transmissionpower levels. More particularly, the present invention relates toestimating transmission power levels in networks such as hybrid fibrecoaxial (HFC) networks for communications between a cable network headend and a cable modem.

2. Description of the Related Art

Determining the power characteristics of a cable modem can allow moreefficient transmission between a cable modem and a cable network headend. A cable modem typically receives transmissions at a variety ofdifferent downstream frequencies and transmission power levels. Thedifferent downstream frequencies and transmission power levelscorrespond to internal gain levels particular to that cable modem. Anaccurate characterization of the relationships between downstreamfrequencies, transmission power levels, and internal gain levels can bean important part of providing efficient and effective cable networkoperation.

In typical implementations, the power characteristics of a cable modemare determined by placing the cable modem under exhaustive testprocedures. That is, each individual cable modem is tested with a widevariety of downstream frequencies and transmission power levels todetermine internal gain levels. Many conventional test procedures testand calibrate cable modems using hundreds or thousands of differentcombinations of downstream frequencies and transmission power levels.These test procedures used during manufacturing and calibration of eachindividual cable modem take an extensive amount of time and resources.Accordingly, it is beneficial to provide improved techniques forallowing more efficient determination of power characteristics of acable modem.

SUMMARY OF THE INVENTION

Methods and apparatus are provided for determining transmission powerlevels. The power characteristics of a cable modem family are determinedby testing cable modems in a cable modem family with various downstreamfrequencies and transmission power levels to determine internal gainlevels. The power characteristics of the cable modem family can then bestored in an efficient manner in each cable modem by usinginterpolation. The individual cable modem can then be characterized bytesting the cable modem with a limited set of downstream frequencies andtransmission power levels to determine an internal gain level offset forthat particular cable modem. With the power characteristics table,internal gain level offset, and interpolation, transmission power levelscan be determined during network operation when downstream frequenciesand internal gain levels are known.

According to one embodiment, a method for determining powercharacteristics of a family of cable modems is provided. First internalgain levels associated with a first cable modem in a family of cablemodems are determined across a plurality of frequencies and a pluralityof transmission power levels. Second internal gain levels associatedwith a second cable modem in the first family of cable modems aredetermined across the plurality of frequencies and the plurality ofdownstream transmission power levels. The integrated internal gainlevels are stored in the first cable modem. The integrated internal gainlevels are derived using first and second internal gain levels. Theintegrated internal gain levels represent a first subset of the firstand second internal gain levels.

According to another embodiment, a method for calibrating a cable modemassociated with a cable modem family is provided. A first measuredinternal gain level associated with a cable modem communicating with anexternal node at a first downstream frequency and a first transmissionpower level is determined. A second measured internal gain levelassociated with the cable modem communicating with the external node ata second downstream frequency and a second transmission power level isdetermined. The cable modem is calibrated by comparing the first andsecond measured internal gain levels with stored internal gain levelinformation associated with the cable modem family to determine a gainlevel offset.

According to another embodiment, a method for providing a transmissionpower level to an external node coupled to a cable modem is provided. Ameasured internal gain level associated with communications between acable modem tuner and the cable modem demodulator is determined. Apredetermined gain level offset is used to determine an adjustedinternal gain level. The downstream frequency associated withcommunications between the cable modem and the external node isidentified. Interpolation is used to find a transmission power levelassociated with the downstream frequency and the adjusted internal gainlevel.

Other embodiments of the invention pertain to computer program productsincluding machine readable mediums on which is stored programinstructions, tables or lists, and/or data structures for implementing amethod as described above. Any of the methods, tables, or datastructures of this invention may be represented as program instructionsthat can be provided on such computer readable media.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, whichare illustrative of specific embodiments of the present invention.

FIG. 1 is a diagrammatic representation of a network that can use thetechniques of the present invention.

FIG. 2 is a diagrammatic representation of a fibre node.

FIG. 3 is a diagrammatic representation of a cable modem.

FIG. 4 is a graphical representation showing the relationships betweeninternal gain levels, frequency, and transmission power levels.

FIG. 5 is a process flow diagram showing techniques for determining thepower characteristics of a cable modem family.

FIG. 6 is a table representation showing linear interpolation.

FIG. 7 is a flow process diagram showing the calibration of a cablemodem.

FIG. 8 is a flow process diagram showing techniques for determiningtransmission power levels.

FIG. 9 is a diagrammatic representation of a cable modem terminationsystem that can be used with the techniques of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Cable modems in the cable network typically receive transmissions from acable network head end at particular downstream frequencies andtransmission power levels. To allow reliable transmissions between thecable network head end and the cable modem, a cable modem can providetransmission power level information to the cable network head end.However, typical cable modems do not have a transmission power leveldetector. Cable modems, however, do have internal gain levelmeasurements that roughly correspond to transmission power levels atparticular frequencies. The internal gain levels vary as a function oftransmission power levels and downstream frequencies. If the internalgain levels and the downstream frequencies are known, transmission powerlevels can be determined and provided to a cable network head end.

To allow a cable modem to make a determination of transmission powerlevel based on downstream frequency and internal gain levels, powercharacteristics of cable modems are typically determined beforehand inan exhaustive manner. In many conventional implementations, eachindividual cable modem is placed as a unit under test and providedextensive combinations of transmission power levels and frequency inputsto determine internal gain levels. The exhaustively determined valuescan then be stored in the cable modem and provided to a cable networkhead end. However, exhaustively determining power characteristics of acable modem often entails testing a cable modem under hundreds ofthousands of different combinations of transmission power levels anddownstream frequencies. The extensive determination of powercharacteristics can take a large amount of time and resources duringmanufacturing and calibration of each cable modem.

The techniques of the present invention recognize that cable modems in acable modem family often have similar power characteristics. Techniquesare provided for determining the power characteristics of a cable modemfamily and storing the power characteristics of the cable modem familyin each individual cable modem in an efficient manner usinginterpolation. Variations between cable modems in a cable modem familycan be compensated for by determining an internal gain level offset bymeasuring a smaller number of combinations of downstream frequency,internal gain levels, and transmission power levels. According tovarious embodiments, fewer than six combinations can be tested in orderto accurately characterize a cable modem. Upon characterizing the cablemodem, transmission power levels can be provided when downstreamfrequencies, internal gain levels, and internal gain level offsets areknown.

FIG. 1 is a diagrammatic representation of one example of a system thatcan use the techniques of the present invention. A cable network 100includes a cable network head end 102 that provides a communicationinterface between cable modems in the cable network and other networknodes. A cable network head end 102 is typically maintained by aMultiple Service Operator (MSO). The cable modems typically reside atthe subscriber premises 110 a–d.

Each cable network head end 102 can be connected to one or more hubs104. Each hub is configured to service one or more fibre nodes 106 inthe cable network. Each fibre node is, in turn, configured to serviceone or more subscriber groups 110. A primary function of the fibre nodes106 is to provide an optical-electronic signal interface between thecable network head end 102 and the plurality of cable modems residing atthe plurality of subscriber groups 110.

Communication between the cable network head end 102, hub 104, and fibrenode 106 a is typically implemented using modulated optical signals thattravel over fibre optic cables. More specifically, during thetransmission of modulated optical signals, multiple optical frequenciesare modulated with data and transmitted over optical fiber node such as,for example, optical fibre links 103 and 105 a and 105 b are typicallyreferred to as “RF fiber nodes”.

The modulated optical signals transmitted from the cable network headend 102 eventually terminate at the fibre node 106 a. The fibre nodesmaintain the RF modulation during conversion between fibre and coaxmedia.

FIG. 2 is a diagrammatic representation of one example of a conventionalfibre node 106 a of FIG. 1. In conventional cable networks, the fibrenode 200 is responsible for converting RF modulated wavelength opticalsignals into electrical signals and vice versa. The RF modulated opticalsignals enter the fibre node 200 via downstream RF fibre 205, and areconverted into electric signals by the optical-to-electric signalconverter 202. The electrical signals are then amplified by downstreamamplifier 204. The amplified electric signals are then passed to adiplexor 210 that transmits the electric signals over the coaxial line209 to the plurality of cable modems.

In the reverse direction, the cable modems transmit electrical signalsvia the coaxial line 209 to the fibre node 200. The upstream electricalsignals from the cable modems are received at the diplexor 210, andpassed to the upstream amplifier 206. The upstream electrical signalsare then passed from the amplifier 206 to an electric-to-optical signalconverter 208, which converts the upstream electric signals into radiofrequency wavelength modulated optical signals which are thentransmitted to the cable network head end via upstream RF fibre 207.

The cable modem tuner is configured to communicate with the cablenetwork head end 102 through a fibre node at particular downstreamfrequencies and transmission power levels. The frequencies and powerlevels used by a cable modem to communicate through a cable network suchas a Hybrid Fibre Coaxial (HFC) network are referred to herein asdownstream frequencies and transmission power levels, respectively.Typical downstream frequencies lie between 93 MHz and 855 MHz andtypical transmission power levels lie between −20 dB and +20 dB althoughother downstream frequencies and transmission power levels arecontemplated. To allow reliable service for applications such as video,voice, and data, a cable modem tuner maintains particular transmissionpower levels while communicating through the cable network at aparticular downstream frequency.

However, many elements in a Hybrid Fibre Coaxial (HFC) network canaffect power levels and reliable service. Some factors arenon-calibrated downstream or upstream amplifiers, deterioration ofnetwork lines or network nodes, and impedance mismatches created byadded stubs. It would be beneficial to provide transmission power levelsto an MSO in order to allow more reliable service as well as moreeffective diagnosis and maintenance of problems with the HFC network ingeneral and with individual subscribers in particular.

In typical cable modems, however, the tuner does not have a transmissionpower level detector. Typical cable modems, however, do have internalgain levels that are indicative of transmission power levels. Internalgain levels will be described in more detail below. Cable modems alsogenerally have a downstream frequency indicator.

FIG. 3 is a diagrammatic representation of a cable modem having aninternal gain level indicator. According to specific embodiments, acable modem 303 has a cable port 301 to connect the cable modem with ahead end. It also has a tuner 305, modulator 337, demodulator 319,processor 335, memory 323, and USB 327, Ethernet 329, or telephony 331ports to connect the cable modem to client hardware. It should be notedthat multiple components of a cable modem may be contained in a singleintegrated circuit, or may be a combination of digital and analogcircuitry. According to various embodiments, the tuner 305 is a separatecomponent associated with a nonvolatile memory 333.

Tuner 305 typically includes an upstream circuit for transmitting datato a head end and a downstream circuit for receiving data from the headend. The tuner can accommodate both functions through a diplexerconnected to a single cable port. Downstream data sent to the cablemodem from a head end is amplified using an RF amplifier 311. RFamplifier 311 is connected to a mixer 313 coupled with a phase lock loop321. The phase lock loop 321 coupled with the mixer 313 selects achannel and converts the RF signal into an IF signal. According tovarious embodiments, the tuner also contains a downstream frequencyindicator 355 coupled to the phase lock loop 321. The IF signal ispassed through a filter 315 and amplified by an IF amplifier 317. The IFsignal is introduced into a demodulator/receiver 319. Thedemodulator/receiver 319 contains components for analog to digitalconversion, demodulation, frame synchronization, and error correction.

In typical implementations, the demodulator 319 receives signals fromthe tuner 305 at a set power level. To maintain the set power level, thedemodulator 319 provides feedback signals to the tuner 305 to adjust theamount of amplification applied during the conversion of the RF signalto an IF signal. According to various embodiments, the feedback signalsare IF AGC and RF AGC values contained in registers 351 and 353. Intypical implementations, when the transmission power levels are higher,the internal gain levels such as the IF AGC and RF AGC values are lower.That is, when the transmission power levels are higher, lessamplification of the signal is applied at the tuner 305 before providinga frequency converted signal to the demodulator 319. Values foradjusting the power level of the signal provided to the demodulator arereferred to herein as the internal gain levels. In one embodiment, theinternal gain level is the sum of IF AGC and RF AGC.

The downstream data transmission is then passed to a processor 335connected to memory 323. A processor 335 may be a general purpose CPU ora specially configured ASIC. According to specific embodiments, theprocessors encapsulate and decapsulate packets within a MAC header,preferably according to the DOCSIS standard for transmission of data orother information. The encapsulation and decapsulation can be performedby processor 335 coupled with memory 323 or by special purpose MAChardware. The transmission is then passed to local interface 325comprising ports supporting protocols and standards such as USB,Ethernet, PCI, and telephony.

A client wishing to send data upstream through the cable modem does sothrough interface 325. The packets are processed and encapsulated byprocessor 335 coupled with memory 323 and passed to the upstreammodulator/transmitter 337. The processor 335 can also time thetransmissions of the upstream bursts. The modulator/transmitter encodesthe data, modulates the data onto a selected frequency, and converts thesignal from digital to analog. The signal is filtered at 339 and passedon to a variable reverse amplifier 341 before transmitting the signalthrough diplexer 309 onto the cable network.

The transmitter circuitry of the cable modem typically has variablereverse amplifier 341, filter 339, and the modulator/transmitter 337.Cable modems can also have enable and disable functionality fortransmitter circuitry. The transmit enable and disable states allow thecable modem to put the transmitter circuitry in standby mode, so thatthe cable modem consumes less power when no data needs to be transmittedto the head end.

Receiver circuitry 307 of the cable modem contains RF amplifier 311,phase lock loop 321, mixer 313, filter 315, and IF amplifier 317.Receiver circuitry 307 can additionally comprise processors, memory, andMAC hardware.

FIG. 4 is a graphical representation showing the relationship betweentransmission power levels 411, downstream frequency 413, and internalgain levels 415. As noted above, internal gain levels can be used foradjusting the amplification of signals provided to the demodulator fromthe tuner. Typically, internal gain levels decrease as transmissionpower levels increase. In one example, the amplification of the internalsignal level from tuner to the demodulator does not need to be as highwhen the transmission power level at the tuner is already high.

Internal gain levels and transmission power levels can also vary as afunction of frequency. It should be noted that many tuners includedifferent amplifiers for different frequency bands. In one embodiment,an amplifier stage is provided for each of the different UHF, VHF low,and VHF high bands. Within a single band, increases in frequencytypically correspond to lower internal gain levels or highertransmission power levels. The relationships between internal gainlevels, downstream frequencies, and transmission power levels aretypically similar in cable modems in a family of cable modems. However,some differences remain even between cable modems in a cable modemfamily. In one example, the relationship between downstream frequency,transmission power levels, and internal gain levels in cable modemswithin a single cable modem family differ by an internal gain leveloffset. Any value for determining power characteristics of the cablemodem in relation to the cable modem family is referred to herein as aninternal gain level offset. By recognizing the characteristics of thefamily of cable modems, many characteristics of the particular cablemodem in the cable modem family can be recognized.

In particular, having two of the three variables known in the powercharacteristics table can allow a determination of the third variable.According to various embodiments, if the internal gain levels can beascertained by reading IF AGC and RF AGC values, for example, and thedownstream frequency can be ascertained by reading a downstreamfrequency indicator, transmission power levels can be determined.Transmission power levels can then be stored and provided to a multipleservice operator in order to ensure reliable data transmission.

FIG. 5 is a process flow diagram showing techniques for determining thepower characteristics of a cable modem family. At 501, a cable modem ina cable modem family is treated as a unit under test. According tovarious embodiments, the cable modem at 503 is fed signals atfrequencies between 93 MHz and 855 MHz in 6 Mhz steps along power levelsbetween −20 dB and +20 dB in 1 dB steps. It should be noted that thetechniques of the present invention contemplate a variety of frequencybands, power bands, frequency increments, and power increments. Theinternal gain levels can then be read at each downstream frequency andtransmission power level combination at 505 to yield a data structurehaving 41 transmission power level entries by 128 downstream frequencyentries. In one embodiment, this 5248 entry table has 41 rowsrepresenting transmission power levels from −20 dB to +20 db and 128columns representing downstream frequencies from 93 MHz to 855 MHz. Thisprocess can be repeated for a number of different tuners and the familyof cable modems to acquire internal gain levels for multiple cablemodems at 507. At 509, the internal gain levels for each downstreamfrequency and transmission power level combination can be averaged. Inone embodiment, errant values are discarded. At this point, the valuescan be stored in a cable modem in and the cable modem family as a fairlyaccurate characterization of the cable modem and the tuner. However, thenumber of values at this point is large. It would take a large amount ofmemory in the cable modem to store a 5248 entry data structure.

One solution to reduce the amount of memory needed in the cable modem tostore power characteristics of the cable modem family is to useinterpolation. The techniques of the present invention allow theefficient storage of power characteristics information for a cable modemfamily by using interpolation at 511. In one example, linearinterpolation can be used to determine where internal gain levelvariations along downstream frequency and transmission power levels arelinear. By recognizing what internal gain levels can be interpolatedfrom surrounding internal gain levels, the table size can be reducedsignificantly. According to various embodiments, it is recognized thatvariations in internal gain levels are linear across frequency bandsusing the same amplifier stage. In one example, variations in internalgain levels are roughly linear across the UHF band, the VHF low band,and the VHF high band. By maintaining internal gain levels at the endpoints of these various frequency bands, internal gain levels betweenthe end points of these various frequency bands can be interpolatedusing linear interpolation.

FIG. 6 is a table representation simplified to show linear interpolationthat may be applicable to determining the relationships betweendownstream frequency, transmission power levels, and internal gainlevels. In this simplified example, the internal gain level valuesranging from 20 k to 90 k vary linearly across downstream frequenciesvarying from 100 MHz to 200 Mhz and linearly across transmission powerlevels ranging from 10 dB to 0 dB. Even if the values in column 603 ornot stored in a power characteristics table, the values in column 603could be linearly interpolated by using the values in column 601 and thevalues in column 605. Similarly, even if the values in row 613 weredeleted, the values in row 613 could be linearly interpolated by usingthe values in row 611 and the values in row 615.

By using linear interpolation, fewer values for internal gain levels,transmission power levels, and downstream frequencies can be storedwhile maintaining an accurate characterization of the cable modemfamily. Internal gain levels, transmission power levels, and downstreamfrequency levels characterizing the cable modem family that aremaintained in a cable modem are referred to herein as stored internalgain levels, stored transmission power levels, and stored downstreamfrequencies. Any data structure for maintaining the stored internal gainlevels, stored transmission power levels, and stored downstreamfrequencies is referred to as a power characteristics table. Accordingto various embodiments, the power characteristics table contains fivedownstream frequency columns roughly corresponding to the borders of theUHF, VHF low, and VHF high bands and 41 rows representing transmissionpower levels from −20 dB to +20 dB in 1 dB increments.

It should be noted that although the downstream frequency columnsmaintained can be those that roughly correspond to the borders of thedifferent frequency bands, the downstream frequencies columns maintainedcan be determined automatically or manually by inspecting the internalgain level values for linear characteristics. It should also be notedthat other types of interpolation can be used as well. In one example,logarithmic or higher order interpolation can be used. Relationships canbe represented using two or more variables.

As noted above the characteristics of the cable modem family can bedetermined quickly and stored efficiently in each cable modem by usinginterpolation. Each cable modem no longer needs to be tested with a widerange of downstream frequency and transmission power levels to determineinternal gain levels. Instead, internal gain levels for the range ofdownstream frequencies and transmission power levels are determined oncefor a cable modem family and stored in an efficient manner in each cablemodem using interpolation. However, each cable modem within a cablemodem family may have slightly different characteristics than othercable modems within the cable modem family. The techniques of thepresent invention recognize that individual cable modems in a cablemodem family typically vary by an offset. In one example, a particularcable modem in a cable modem family may have internal gain levels thatare 10 units higher than another cable modem in the cable modem familyfor the various downstream frequencies and transmission power levels. Inorder to allow effective characterization of each cable modem by usingthe power characteristics of the cable modem family, an offset isdetermined.

FIG. 7 is a flow process diagram showing the calibration of a cablemodem by using an offset to adjust for variance within a cable modemfamily. According to various embodiments, the cable modem can be treatedas a unit under tested and provided signals across a wide range ofdownstream frequencies and transmission power levels to determineinternal gain levels. The internal gain levels can then be comparedagainst the stored internal gain levels associated with a cable modemfamily to determine an offset. However, this technique can betime-consuming and reduces the benefits of using power characteristicsof the cable modem family to characterize the cable modem. Instead, ifyou selected downstream frequencies can be provided to the cable modemat a set transmission power level to determine internal gain levels atthat particular transmission power level. The internal gain levels atthat particular transmission power level can then be compared to bestored internal gain levels associated with the cable modem family todetermine an offset. The offset can then be applied to all internal gainlevels across the range of downstream frequencies and transmission powerlevels.

At 701, the cable modem is provided 5 downstream frequencies all at a 0dB transmission power level. According to various embodiments, the fiveinternal gain levels corresponding to the five downstream frequencies atthe 0 dB transmission power level are determined at 703. The fiveinternal gain levels at 705 are compared against the stored internalgain levels in the power characteristics table associated with the cablemodem family. An offset is determined in one example by averaging thedifferences at 707. It should be noted that interpolation can be used atthis point to determine stored internal gain levels for frequencies thatare not represented in the power characteristics table. Similarly,interpolation could be used at this point to determine stored internalgain levels for transmission power levels that are not represented inthe power characteristics table. The offset is stored in the cablemodem. The offset can be applied to all of the values in the powercharacteristics table or can be dynamically applied to any value readfrom the cable modem. In one example, the offset can be applied to AGCvalues read from the demodulator.

It should be noted that the offset can be represented in a variety ofdifferent manners. Although an internal gain level offset could beconveniently applied, offsets can also be applied to downstreamfrequencies and transmission power levels to reach the same effect or tofurther fine-tune the characterization of the cable modem using thepower characteristics table.

After an offset is determined, the particular cable modem can beeffectively characterized without putting the cable modem through anextensive unit under test analysis across a wide range of frequenciesand a wide range of transmission power levels. As noted above, intypical implementations each individual cable modem is painstakinglyplaced as a unit under test to determine power characteristics by usingan exhaustive range of downstream frequencies, transmission powerlevels, and internal gain levels. According to the techniques of thepresent invention, power characteristics for a cable modem family aredetermined and stored in the cable modem. Each cable modem then can betested for a limited set of downstream frequencies, transmission powerlevels, and internal gain levels to determine power characteristics. Intypical implementations hundreds to thousands of combinations ofdownstream frequencies, transmission power levels, and internal gainlevels would have to be tested.

According to various embodiments of the present invention, fewer thanten combinations could be tested to determine power characteristics ofthe cable modem by characterizing the cable modem family before hand.Each individual cable modem can then be characterized against the cablemodem family by testing fewer than six combinations, although more canbe tested while still falling within the scope of the present invention.The selected downstream frequency and transmission level combinationscan be used to determine the offset of the particular cable modem fromthe cable modem family in an efficient in effective manner that meetsthe requirements of DOCSIS 1.1, available from Cable TelevisionLaboratories, Louiseville, Colo.

FIG. 8 is a flow process diagram showing techniques for determiningtransmission power levels after a cable modem has been calibratedaccording to the techniques of the present invention. At 801, themeasured internal gain level is identified. According to variousembodiments, identifying the internal gain level may entail reading andadding the IF AGC and RF AGC values in registers associated with thedemodulator. At 803, the internal gain offset can be added to themeasured internal gain level to determine the adjusted internal gainlevel. At 805, the downstream frequency can be determined by reading thedownstream frequency indicator associated with the tuner. At 807, thepower characteristics table can be referenced using the downstreamfrequency and the adjusted internal gain level to determine thetransmission power level. It should be noted that interpolation such aslinear interpolation can be used to determine transmission power levelsfor downstream frequencies and internal gain levels that are notexplicitly stored in the power characteristics table. At 809, thetransmission power level can be stored and/or provided to the cablenetwork head end to allow more efficient and effective operation of thecable network.

In the context of a cable network, the invention can be implemented in acable modem coupled with a cable modem termination system, such as Cisco6920 RateMux® available from Cisco Systems, Inc, or in a line card of acable modem head end such as the Cisco UBR 7200 also available fromCisco Systems, Inc.

FIG. 9 depicts the basic components of a cable modem head end that canbe coupled with a cable modem. A Data Network Interface 902 is aninterface component between an external data source and the cablesystem. External data sources transmit data to data network interface902 via optical fibre, microwave link, satellite link, or throughvarious other media. Also as mentioned above, a Media Access ControlBlock (MAC Block) 904 receives data packets from a Data NetworkInterface 902 and encapsulates them with a MAC header.

In a specific embodiment as shown in FIG. 9, CMTS 900 provides functionson three network layers including a physical layer 932, a Media AccessControl (MAC) layer 930, and a network layer 934. Generally, thephysical layer is responsible for receiving and transmitting RF signalson the cable plant. Hardware portions of the physical layer include adownstream modulator and transmitter 906 and an upstream demodulator andreceiver 914. The physical layer also includes software 986 for drivingthe hardware components of the physical layer.

Once an information packet is demodulated by the demodulator/receiver914, it is then passed to MAC layer 930. A primary purpose of MAC layer930 is to encapsulate and decapsulate packets within a MAC header,preferably according to the above-mentioned DOCSIS standard fortransmission of data or other information.

MAC layer 930 includes a MAC hardware portion 904 and a MAC softwareportion 984, which function together to encapsulate information packetswith the appropriate MAC address of the cable modem(s) on the system.After the upstream information has been processed by MAC layer 930, itis then passed to network layer 934. Network layer 934 includesswitching software 982 for causing the upstream information packet to beswitched to an appropriate data network interface on data networkinterface 902.

When a packet is received at the data network interface 902 from anexternal source, the switching software within network layer 934 passesthe packet to MAC layer 930. MAC block 904 transmits information via aone-way communication medium to downstream modulator and transmitter906. Downstream modulator and transmitter 906 takes the data (or otherinformation) in a packet structure and converts it to modulateddownstream frames, such as MPEG or ATM frames, on the downstream carrierusing, for example, QAM 64 modulation (other methods of modulation canbe used such as CDMA (Code Division Multiple Access) OFDM (OrthogonalFrequency Division Multiplexing), FSK (FREQ Shift Keying)). The returndata is likewise modulated using, for example, QAM 16 or QSPK. Data fromother services (e.g. television) is added at a combiner 907. Converter908 converts the modulated RF electrical signals to optical signals thatcan be received and transmitted by a Fibre Node 910 to the cable modemhub.

It is to be noted that alternate embodiments of the CMTS (not shown) maynot include network layer 934. In such embodiments, a CMTS device mayinclude only a physical layer and a MAC layer, which are responsible formodifying a packet according to the appropriate standard fortransmission of information over a cable modem network. The networklayer 934 of these alternate embodiments of CMTS devices may beincluded, for example, as part of a conventional router for apacket-switched network.

In a specific embodiment, the network layer of the CMTS is configured asa cable line card coupled to a standard router that includes thephysical layer 932 and MAC layer 930. Using this type of configuration,the CMTS is able to send and/or receive IP packets to and from the datanetwork interface 902 using switching software block 982. The datanetwork interface 902 is an interface component between external datasources and the cable system. The external data sources transmit data tothe data network interface 902 via, for example, optical fibre,microwave link, satellite link, or through various media. The datanetwork interface includes hardware and software for interfacing tovarious networks such as, for example, Ethernet, ATM, frame relay, etc.

As shown in FIG. 9, the CMTS includes a hardware block 950 including oneor more processors 955 and memory 957. These hardware componentsinteract with software and other hardware portions of the various layerswithin the CMTS. Memory 957 may include, for example, I/O memory (e.g.buffers), program memory, shared memory, etc. Hardware block 950 mayphysically reside with the other CMTS components.

Because such information and program instructions may be employed toimplement the systems/methods described herein, the present inventionrelates to machine readable media that include program instructions,state information, etc. for performing various operations describedherein. Machine readable media may contain instructions for programmingtuner characteristics onto a nonvolatile memory. Examples ofmachine-readable media include, but are not limited to, magnetic mediasuch as hard disks, floppy disks, and magnetic tape; optical media suchas CD-ROM disks; magneto-optical media such as optical disks; andhardware devices that are specially configured to store and performprogram instructions, such as read-only memory devices (ROM) and randomaccess memory (RAM). Aspects of the invention may also be embodied in acarrier wave travelling over an appropriate medium such as airwaves,optical lines, electric lines, etc. Examples of program instructionsinclude both machine code, such as produced by a compiler, and filescontaining higher level code that may be executed by the computer usingan interpreter.

While the invention has been particularly shown and described withreference to specific embodiments thereof, it will be understood bythose skilled in the art that changes in the form and details of thedisclosed embodiments may be made without departing from the spirit orscope of the invention. For example, the embodiments described above maybe implemented using firmware, software, or hardware. Moreover,embodiments of the present invention may be employed with a variety ofcommunication protocols and should not be restricted to the onesmentioned above. For example, the head end has a variety of embodiments,which include a cable modem termination system coupled to a router or amulticast router. A cable modem can also be a separate entity orentirely integrated into a client system. Therefore, the scope of theinvention should be determined with reference to the appended claims.

1. A method for determining power characteristics of a family of cablemodems, the method comprising: determining first internal gain levelsassociated with a first cable modem in a family of cable modems across aplurality of frequencies and a plurality of transmission power levels;determining second internal gain levels associated with a second cablemodem in the first family of cable modems across the plurality offrequencies and the plurality of downstream transmission power levels;storing integrated internal gain levels in the first cable modem, theintegrated internal gain levels derived using first and second internalgain levels, wherein the integrated internal gain levels represent afirst subset of the first and second internal gain levels.
 2. The methodof claim 1, wherein first internal gain levels are used for adjustinginternal power levels between a tuner and a demodulator associated withthe first cable modem.
 3. The method of claim 2, wherein the downstreamtransmission power levels are power levels between the tuner and anexternal node.
 4. The method of claim 3, wherein the first internal gainlevels are a combination of IFAGC and RFAGC values.
 5. The method ofclaim 3, wherein the first subset of the first and second internal gainlevels comprises first and second internal gain levels across a secondsubset of the plurality of frequencies.
 6. The method of claim 5,wherein the second subset is five frequencies between 93 MHz and 855MHz.
 7. The method of claim 5, wherein the integrated internal gainlevels between the subset of the plurality of frequencies can bedetermined substantially by using linear interpolation.
 8. The method ofclaim 5, wherein the first subset of the first and second internal gainlevels comprises first and second internal gain levels across a thirdsubset of the plurality of power levels.
 9. The method of claim 8,further comprising determining third internal gain levels associatedwith a third cable modem across a plurality of frequencies and aplurality of transmission power levels.
 10. The method of claim 8,wherein the integrated internal gain levels are derived by averaging thefirst and second internal gain levels.
 11. The method of claim 10,wherein the integrated internal gain levels are stored in volatilememory associated with the cable modem.
 12. A method for calibrating acable modem associated with a cable modem family, the method comprising:determining a first measured internal gain level associated with a cablemodem communicating with an external node at a first downstreamfrequency and a first transmission power level; determining a secondmeasured internal gain level associated with the cable modemcommunicating with the external node at a second downstream frequencyand a second transmission power level; calibrating the cable modem bycomparing the first and second measured internal gain levels with storedinternal gain level information associated with the cable modem familyto determine a gain level offset.
 13. The method of claim 12, whereinthe first and second power levels are both 0 dB.
 14. The method of claim13, wherein stored internal gain level information comprises internalgain levels associated with the cable modem family.
 15. A computerreadable medium comprising computer code for calibrating a cable modemassociated with a cable modem family, the computer readable mediumcomprising: computer code for determining a first measured internal gainlevel associated with a cable modem communicating with an external nodeat a first downstream frequency and a first transmission power level;computer code for determining a second measured internal gain levelassociated with the cable modem communicating with the external node ata second downstream frequency and a second transmission power level;computer code for calibrating the cable modem by comparing the first andsecond measured internal gain levels with stored internal gain levelinformation associated with the cable modem family to determine a gainlevel offset.
 16. The computer readable medium of claim 15, wherein thefirst and second power levels are both 0 dB.
 17. The computer readablemedium of claim 16, wherein stored internal gain level informationcomprises internal gain levels associated with the cable modem family.18. A method for providing a transmission power level to an externalnode coupled to a cable modem, the method comprising: determining ameasured internal gain level associated with communications between acable modem tuner and the cable modem demodulator; using a predeterminedgain level offset to determine an adjusted internal gain level;identifying the downstream frequency associated with communicationsbetween the cable modem and the external node; using interpolation tofind a transmission power level associated with the downstream frequencyand the adjusted internal level.
 19. The method of claim 18, whereinusing interpolation comprises using linear interpolation between storeddownstream transmission frequencies in an internal gain table.
 20. Themethod of claim 19, wherein using interpolation comprises using linearinterpolation between stored transmission power levels.
 21. The methodof claim 18, wherein the gain level offset is programmed intononvolatile memory.
 22. The method of claim 21, wherein identifying thedownstream transmission frequency comprises reading the downstreamtransmission frequency from a MAC device associated with the tuner. 23.The method of claim 22, wherein using the gain level offset to determinethe adjusted internal gain level comprises combining the measuredinternal gain level with the gain level offset.
 24. The method of claim22, wherein using the gain level offset to determine the adjustedinternal gain level comprises combining the measured internal gain leveloffset with the stored internal gain level values associated with thecable modem family.
 25. The method of claim 24, wherein the storedinternal gain level values are predetermined AGC values stored in atable in memory across a plurality of frequencies and a plurality oftransmission power levels.
 26. The method of claim 25, wherein theplurality of frequencies lie between 93 MHz and 855 MHz.
 27. The methodof claim 26, wherein the plurality of transmission power levels liebetween −20 dB and +20 dB.
 28. A cable modem coupled to an externalnode, the cable modem comprising: means for determining a measuredinternal gain level associated with communications between a cable modemtuner and the cable modem demodulator; means for using a predeterminedgain level offset to determine an adjusted internal gain level; meansfor identifying the downstream frequency associated with communicationsbetween the cable modem and the external node; means for usinginterpolation to find a transmission power level associated with thedownstream frequency and the adjusted internal gain level.
 29. The cablemodem of claim 28, wherein using interpolation comprises using linearinterpolation between stored downstream transmission frequencies in aninternal gain table.
 30. The cable modem of claim 29, wherein usinginterpolation comprises using linear interpolation between storedtransmission power levels.
 31. The cable modem of claim 28, wherein thegain level offset is programmed into nonvolatile memory.
 32. The cablemodem of claim 31, wherein identifying the downstream transmissionfrequency comprises reading the downstream transmission frequency from aMAC device associated with the tuner.
 33. The cable modem of claim 32,wherein using the gain level offset to determine the adjusted internalgain level comprises combining the measured internal gain level with thegain level offset.
 34. The cable modem of claim 32, wherein using thegain level offset to determine the adjusted internal gain levelcomprises combining the measured internal gain level offset with thestored internal gain level values associated with the cable modemfamily.
 35. The cable modem of claim 34, wherein the stored internalgain level values are predetermined AGC values stored in a table inmemory across a plurality of frequencies and a plurality of transmissionpower levels.
 36. The cable modem of claim 35, wherein the plurality offrequencies lie between 93 MHz and 855 MHz.
 37. The cable modem of claim36, wherein the plurality of transmission power levels lie between −20dB and +20 dB.